Variable timing circuit



Feb. 20, 1951 H. MICRAIN 2,542,631

VARIAB LE TIMING CIRCUIT Filed July 23, 1946 2 Sheets-Sheet l gRla INVENTOR. HARRY M. GRAIN AT TOR NEY Feb. 20, 1951 M, cRAlN 2,542,631

VARIABLE TIMING CIRCUIT Filed July 23, 1946 2 Sheets-Sheet 2 FIRE CUTOFF Fl GUTOFF INVENTOR. HARRY M. GRAIN ATTORNEY V2 WE F/G. 2 F /6.3.

Patented Feb. 20,

VARIABLE TIMING QERCIJIT Harry M. Crain san Diego,0alif., assignor to-the United States of America as represented by the Secretaryof thez-Nayy Applieationjuly 23, 1946, Serial No. 685,533

10 Glaims.

The-present invention relates in general to timing circuits and is more specifically concerned with improved novel means 'for efiecting variations in the time interval.

Timing circuits of the herein described type are susceptible of many uses for obtainingdesired operations at a predetermined time interval. One such use is in the production of pulses at timed intervals for the simulation of delayed target echoes in connection with sound training equipment.

In such timing circuits, means are usually provided for adjustingthe extent of the time interval. The conventional means utilized in certain prior art systems for adjusting the time interval do not permit quick adjustment and in some cases a laghas'been exhibited. For example, following an adjustment for lengtheningthe timing interval, each of the next few cycles will be longer than its predecessor, until the system settles down at the new time interval.

To overcome the above and inherent disadvantages of I the timing circuits as heretofore arranged, the present invention contemplates as a primary object the provision of improved means for controllingthe extent of time interval, and means for itsadjustment which-are simple, immediately efiective, and may be made at any time, even after the initial starting impulse has been applied.

A still further object is to provide a timing-circuit having a rapid return to normal conditions.

Briefly, the present invention utilizes a condenser, charging resistor, and voltage source of of output voltage pulses obtainable at different points of the circuit for two 'difieren-t time inter-' vals.

Referring now to Figure 1 of the drawings, the connection of the various elements and their 015- era-tion as embodied in the timing circuit of the present invention will be explained. The timing circuit uti=lizes a normally non-conducting gas tube VI connected in se ries with a triode V2. Although the latter of these tubes is ready to conduct, it cannot conductbeeauseit in series with tube Vi which will conduct only when a pulse or" proper polarity and magnitudeis 319191165 to it control rid! v plate of tube s connfiQ ed in circuit with 'a resistor 3.7, which serves when energized by means of two pulses, an initial starting pulse and a second terminating pulsethe time ofoccurrence of the latter being dependent upon the condenser charging rate voltage reaching a predetermined value. -A simple potentiometer is provided for varyingthepoint-at which thecon denser charging voltage will be interrupted, and

this action is utilized to trigger the means for producing the second pulse.

The features of novelty which I- believeto be characteristic of my invention are set forth with 1 particularity in the appended claims. invenducting with the result that a current .fiow .-is'

will best be understood byreference-to the speci-S fication and accompanying drawings in which-:

Figurel is a circuit diagramof a-timingcircuitembodying the features of the present invention:

and

"Figures 2 -and13 illustrate the -respectiveiorms through resistor RH andfiitsto ground potent al o a v l our or h gin a timing 99adenser 03 through a charging resistorBS. With a constant potential supplied by the resistor R? n prqperly s ficted've ues'for th mea e. sistor and its condenser, the charging rate will always, be the same with the charging time interval determined by the value of resistor Rt.

A referenee voltage is established across the condenser C3 by means of a gas tube. V3 which ma ne eentinue sl thr h re r R3 and 5, 0 cenn et i t-. h j ii asrtd a l ea tput v l a e a rea e lt d d r-ma of series connecteddiode V4 and triode V5.'

x ill al be e e t e n th teem-H shown, the condenser C3 is shunt connected in relation to tube V5, and the resistor R? and sistor R9 form ,a shunt path in relation to ,tube V4.

, The control grid ,of tube V5 is .conn

so that with no current flowing through these sisters, the grid will be at zero-potential. plate of tube V2 isconnectedjthrougna conductor It and condenser CI to apo int between resistors RH andBB.

..T e o erat f the. eme ts i hu er er b d i char n emdease C will b e e lewsi Upo t e ei t e ms iv 'pl lse the control grid of gas tube VI, this tube begins con established through resistor 3.5, triode lij and resistor R3. Since the tube :Vl is a gastube, its grid immediately loses-control and can-not infi-ur; ence the operation further.

.Priorto theestablishment of the above current flow, charging .oicondenser Cl through re;

cooperation with tubes V3 .and 1 N4 establish, the

reference voltage on-condenser C3.

It will now be evident that as soon as current flow is established through R5, V2, VI and R1, a negative going voltage will be established on the plate of tube V2 which will act through condenser CI to place a negative going pulse on the grid of tube V so that it will stop conducting. At the same time, the voltage appearing across resistor R1 delivers a charging current to timing condenser 03 through its charging resistor R9. The charging voltage of this condenser quickly rises above that across tube V3, so that diode V4 becomes non-conducting. The condenser Cl and resistor R8 have a high enough time constant to maintain triode V5 non-conducting during the timing period, As current flows through resistor R9, the voltage at C3 accordingly will steadily rise as shown at C in Figures 2 and 30f the drawmgs.

Since the condenser C3 has a predetermined charging rate as previously explained, it will be evident that if means are provided which may be adjustable to interrupt the charging cycle of condenser C3, at points along the charging voltage curve of this condenser, the time interval of charge may be varied as desired and utilized for useful purposes. Different time intervals of charging are shown in Figures 2 and 3.

In the present invention, the control of the timing interval and cut-off of the charging operation is accomplished by the use of a cathode follower circuit and multivibrator circuit which will now be explained.

As further shown in Figure 1, the condenser C3 connected in the usual manner through resistor Rl2 to the grid of a cathode follower tube V6 so that the voltage of the condenser C3 may be utilized and is applied as a trigger voltage for the multivibrator tubes V'I.

, Referring to the drawings, it will be seen that the tubes of the multivibrator have their filaments interconnected, and that the plate of the left tube is connected through a condenser C4 and resistor RH, this resistor also being in circuit with the grid of the right tube. The filaments of these two tubes are connected through a conductor l l with the'movable terminal of po-' tentiometer'Pl whichds energized from a suitable source of potential through series resistor j'The right tube normallyconducts current, since its grid is at filament potential. If a in creasing voltage on the grid of the left tube reaches a sufiiciently high potential above its filament, this tube will trigger and starts conducting. This causes a negative going voltage on its plate, which acts through condenser C4 and resistor RI! to apply a negative going voltage on the grid of the right tube, which causes it to cutofi. I. V

The negative-going voltage on the plate of the left tube further acts through conductor l2, a resistor Bi 9 and condenser C2 to impress a negative pulse on the'grid of V2, whereupon this tube cuts-off and interrupts the flow of current through the charging source of potential R1 for the timing condenser C3. g

At the same time, a positively going pulse from the plate of tube V2 acts to again make the tube V5 conducting so that it will drain the timing condenser C3. Since grid of V5 goes positive, it conducts the charge from condenser Cl and thereby permits the system to return to normal in far less time than the charging period of condenser C3. For example, it has been ascertained in actual practice that with. the proper selectionof circuit values, the timing period or charging time for the condenser C3 is adjustable over a range from 0.01 second to 5 seconds and the circuit returns to normal in less than 0.005 second.

The adjustment of the timing period is accomplished through the potentiometer Pl which normally operates to place a positive potential on the filament of the left tube of the multivibrator. By varying the voltage on the filament, the point in the rising voltage of the condenser C3 at which triggering will take place may be determined.

The tubes of the multivibrator may trigger back to normal in response to decrease or drop of voltage at condenser C3 when the condenser is drained by tube V5, or failing to do so, will operate to trigger back to normal when the negative charge has drained ofi condenser Cli through resistor R1! sufiiciently to let the right tube begin conducting again. In any event, it is desirable that the tubes Vl should not trigger back until the condenser C3 has returned to its normal condition, because when so delayed it prevents tube VI from starting a new cycle until the circuit is ready. In the present system, the condenser C3 returns to normal so quickly that there is no difficulty in meeting this requirement.

In the timing circuit of this invention, the timing period may be changed at Pl, even while the condenser C3 is charging without disturbing the operation or introducing errors of any kind. Furthermore, since the grid of tube VI loses control during the timing period, the initiating pulse may be prolonged or repeated without disturbing the operation.

Output voltages may be taken off at points in-' dicated at A, B, C, D and E on the circuit diagram as shown in Figure l. The wave forms of the respective voltage pulses at these points for two different time intervals are shown in Figures 2 and 3. It will be noted that, since the voltage and output point C rises at the same rate for all intervals as determined by the setting of the potentiometer Pi, the peak voltage increases with the time interval. At points A and B, the

timing circuit of this invention has a rapid return to normal,

WhatIclaimis: 1. A timing circuit comprising a condenser having one terminal at ground potential, means for charging the condenser at a predeterminedrate, thyratron triggered control means operativef upon receipt of a first pulse to start operation of the charging means and continuously conducting thereafter regardless of further pulses" received by said control means while said con-.

denser,v is charging, multivibrator means operable to generate a second pulsecontrolled by said.

condenser, triode tube means connected to said condenser for establishing a lower reference po-' tential thereon relative to said ground potential, a cathode follower tube having the cathode thereof connected to a grid of said multivibrator means and resistively connected to said ground potential. andhaving a control grid...the1:eof reasing-cs1 sistively connected to saidcondenser' at the ungro'unded terminal J thereof "and means supplying variable cathode potential to said 'multivibrator, last said means being adjustable-'t'o-vary the time interval between firstand second pulses. 2. A thyratron controlled timing circuit com- 'prising mea ns operable uponenergi'zation to provide a voltage having a predetermined rate of change between lower and upper limits, thyratron control means operable upon receipt of a first pulse to start said energization and upon receipt of a secondpulse 'to" stop said energization independently of duration and variations in said first pulse, a cathode follower circuit having a control grid therein resistively coupled to said voltage producing means'and responsive thereto for controlling the cathode follower voltageoutput, a multivibrator including a'tr'iode tube havit's grid connected to said: cathodef'ollower output and adapted to trigger are; predetermined value thereof, means for varying said upper limit of voltage and the time interval between said lower and upper limits during said interval "and a connection for applying an output from the multivibrator to form the said second pulse.

3. A thyratron controlled timing circuit comprising means operable upon energization to provide a voltage having a predetermined rate of change between lower and upper limits, thyratron control means operable upon receipt of a first pulse to start said energization and upon receipt of a second pulse to stop said energization, a cathode follower tube having a grid thereof resistively coupled to follow said voltage and a cathode resistively coupled to ground potential, a multivibrator including a triode tube having its grid connected to said cathode and adapted to trigger at a predetermined potential thereof,

a connection for applying an output from the multivibrator to form the said second pulse, and a potentiometer in the cathode circuit of said tube for varying the voltage level thereof and the trigger voltage value required to cause the tube to conduct.

4. The timing circuit of claim 1 having means for quickly discharging the condenser to said lower reference potential when the multivibrator circuit is triggered.

5. The timing circuit of claim 1 having means for continuously applying a reference potential across the condenser While the condenser is not charging, means for quickly discharging the condenser to said reference potential when charging thereof is terminated and in which said adjustable means controls the cathode bias potential on the multivibrator tubes.

6. The timing circuit of claim 3 having means responsive to the second pulse for restoring said voltage to said lower limit during the second pulse whereby the circuit is immediately restored to the initial condition.

'7. In a circuit for measuring controlled time intervals from an initial quiescent condition thereof, a condenser, a gaseous discharge tube arranged for continuous discharge for providing a reference potential across the plate and cathode thereof, a pair of vacuum tubes series connected across said reference potential in normally conducting arrangement, means including said pair of tubes for supplying a predetermined initial charge to said condenser, a thyratron tube triggerable by a grid pulse thereto and having the cathode thereof connected through a resistance element to the plate of said discharge tube for impressing a charging voltage on said element while the thyratron -opera'tes',-'means inf:-

eluding a ci-irrent controlling resistance c61 1- nected to the condenser and responsive to the voltage thereon, a multivibrator circuit con nected to said cathode follower circuit and arranged for actuation at a selected voltage'on the condenser, circuit means connected to said multi vibrator and said third vacuum tubeahd responsive to actuation of themultivibrat'or for exting-u'i'shingthe thyratron when the vouageenwe condenser has reached said selected -'voltage, means for resetting the time measuring cir 11132 to saidinitial condition substantially without d' lay after actuation of the "inultivibratorfand means including a potential divider "for co'n trolling the selected voltageat which the "mum- Vibrator is actuated, whereby each said time interval is instantly variable independently of's'aid predetermined rate of charging.

8.. A timing circuit comprising means including a first thyratron having a resistance element in the cathode circuit thereof operable in response to an input signal thereto to provide a continuing constant voltage across said resistance element while said thyratron operates, a timing condenser connected to receive a charge from said voltage, means connecting the resistance element to said condenser for controlling the time interval required for accumulating a predetermined charge thereon, means for establishing a reference potential, a potential divider circuit arranged for supplyin a fixed fraction of said reference potential to the condenser when the condenser is not charging, a control circuit connected to the condenser including a multivibrator operative in response to said predetermined charge on the condenser, means controlled by said control circuit for terminating the operation of the thyratron when said predetermined charge occurs on the condenser, and means responsive to operation of last said means for discharging the condenser substantially instantaneously, whereby the timing circuit is reset for measurement of a further time interval When the thyratron is reoperated.

9. A timing circuit comprising means including a first thyratron and a resistance element in the cathode circuit thereof and operable upon energization of the grid thereof to provide a constant voltage across said resistance element while said thyratron operates, a timing condenser connected to receive a charge from said voltage, means connecting the resistance element to the condenser for limiting the charging thereof to a predetermined rate, means including a second thyratron for establishing a reference voltage on the resistance element, a voltage divider circuit comprising a pair of normally conducting thermionic tubes series connected and arranged to supply a fixed fraction of the reference voltage to the condenser as a base voltage thereon, a control circuit connected to the condenser including a cathode follower and a multivibrator operative in response to a predetermined voltage increase on the condenser, means controlled by said control circuit for terminating the operation of first said thyratron when said voltage increase 0n the condenser occurs, means responsive to operation of last said means for discharging the condenser substantially instantaneously 7 .to' the base voltage, and means for controlling the voltage increase at which the control circuit operates, whereby time intervals controlled by the timing circuit are instantly variable between the limits of control thereof.

10. A timing circuit comprising means including a first thyratron and a resistance element in the cathode circuit thereof and operable upon energization of the grid thereof to provide a constant voltage across said resistance element While the thyratron operates, a timing condenser con- .nected to receive a charge from saidvoltage, means connecting the resistance element to said condenser for limiting the'chargin thereof to a predetermined rate, means for establishing a reference potential, a potential divider circuit comprising a pair of normally conducting thermionic tubes series connected to supp y a minimum fixed fraction of said reference potential to the condenser as a base voltage thereon, a circuit connected to the condenser including a multiv-ibrator operative in response to a predetermined charge on the condenser, means controlled by last said circuit for terminating the operation of first said thyratron when said predetermined charge occurs on the condenser, means responsive to operation of last said means for discharging the condenser substantially instantaneously, and means for controlling the voltage charge on the condenser at which last said circuit operates, whereby time intervals controlled by the timing circuit are instantly variable between the limits of control thereof.

HARRY M. GRAIN,

REFERENCES CITED The following references are of record in the file of. this patent:

UNITED STATES PATENTS Rector Mar. 1, 1949 

